Automatic draft control



g 1952 w. B. STEPHENSON ET AL 2,605,968

AUTOMATIC DRAFT CONTROL I Filed Aug. 17, 1949 4 Sheets-Sheet mo r= William B. Stephenson James 3. Lee J Wflja (BT1- Wag. VJ

Aug. 5, 1952 w. B. STEPHENSON ET AL 2,605,968

AUTOMATIC DRAFT CONTROL Filed Aug. 17, 1949 4 Sheets-Shea! 2 III/III/I/II/IIM mmw William Bitgphenson James 5. Lee- Aug- 1 w. B. STEPHENSON ET'AL 2,605,958

AUTOMATIC DRAFT CONTROL Filed Aug. 17, 1949 4 Sheets-Sheet 5 ill/flfffflll/ NVENT Qu= William B. Stephenson Aug. 5, 1952 w. B. STEPHENSON ET AL 2,605,958

AUTOMATIC DRAFT CONTROL Filed Aug. 17, 1949 4 Sheets-Sheet 4 MHiam B. lgahenson Patented Aug. 5, 1952 UNITED STATES- PATENT 2,605,968 v AUTOMATIQDRAFI QQNTBOIJ Williamfi, Stephenson and James -S.;L e,

.Fo ad m s;

App i at n A gust 17, 1949 ssttie N9 11:1:@8P.4

The present invention relates generally -to lip.- provements in draft controls, and more particularly to such controls for automatically admitting air to a furnace or boiler stack or breeching-to regulate the draft intensity andpreven t an excess flow of air through the combustion chamber of the furnace or boiler.

A general object ofthe invention isto provide a novel draft control which is operable tomaintain a substantially constant predetermined negativepressure in the combustion chamber under all atmospheric conditions, and to effectively close the air intake openingin the furnace stack in the event of sudden positive pressure increase in-the combustionchamber.

A further object of the invention resides :in the provision of a draft contro1 which is. especially efiective in angular installationsand in 00111180.- tion with mobile boiler installationssuch for example as in locomotives and steamships which are subject to roll and pitch.

A further object of the invention is toprovide a novel draft control permitting of installation alternatively in upright or inverted positions ac,- cordingto spacerestrictions.

The objects of the invention thus generally se t'for-th togetherwithother objects'and'ancillary advantages are obtained by the constructions and arrangements shown by way of illustration in the accompanyingdrawingsi-n which:

Figure l is a perspective View ofan automatic draft control embodying the -features of the present invention.

Fig. 2 is a front elevation on an enlargedscale of the draft control shown inFig. 1.

Fig. Sis a iragmentaryyertical section talgen along th e'line 33 in Fig.- -2.

"Fig. 4 is a fragmentary horizontal sectional ,view taken substantially in the planeof line 4--4 in Fig. 3.

:Fig. 5 is a fragmentary horizontal sectional Yi k nr u i an al i th P a s 9. llf fi'ilm 5 in iev i a r gm nta y re r z e s efive i of a lower corner of the swinging irame and ,damper plate of the draft .control illustratecl in th p s ed netfieu is a rag n a t el vation p another form of th automatic draft QQI'ltZZOLiiIIk .bodyine teaun s of th r n -i ve ti -Fig..8-.is a fragmentary verticalsection thronghthe form of the inventionshown inI fig. 7,

Fig 9 is ,afragmentary verticaL section taken .snbtantiallyin the plane of line .9T-9 in v,F i g.. ,8.

Fig- 1. s a iraementa'ry f rq t sl ta eil. q 'silll we te fe m t einveh i e Fig. 11 is a 1 side elevation, ,partlyin section, of the forni of the invention illustrated in :While the {invention is susceptible pr various modificationsl andalternative. constructions, fth' re are shown in the drawings and will herein the described in detaillthe preferred .embo but it is ton be hereb o ii hi iip tied e i e e r ne mo i et wula v the rawiess the novel draftcontrolincliides adiit' l'fl ad v a ope .fllg 1.2 i a ver iq wel I its pref red-fo m th uct (i pfs tially square cross section having at oneo wardly exte din flan e 4 qlllc lfilg eiron irieid therewith fo u o s of s a.v

the ame to them-11 of the-stac :t siteendof theiductlfl-is bordered-by y extending flan e 1L6 defin enia inl s ecies 1 8. I

In accordance w th z he rinventiq .1? $19 3. 2? .device,.generally indicated.by-,-the reierence nu mera1 .20, is provided for the .openin 8, includes means responsive to pressure-changes inthe .stackitoopenrand 9105c, and whenpp tn .admit .air into ,thestack from outside the furnace .and .thereby .eflectstabilization of the dratt at a predetermined value, selectable a desired, :to;

gether with supporting means .thereforvieiifective .to permit proper operationregardless,ofethe position of the. duct,' ..whether in angularly ,dis,pqsed installations oriin .systems .whichare themelves subject to movement.

-ti on, and a damperplate -24 pivotallyIsupported on theirame ZZ -t g'etherivvith vcounterloalancing means, generally designatedi26, forthedamper plate effective "to maintain thesameLn'ormaIIyJin engagement the -frame -22 to close the frame opening 22a. -Provisionis alsomadeltomiriim'ize 1e 1;age of air into theduct-l 0 aboutthe frameizl.v

' :In'fthe firstof --the eiieniplary embodimentsof the invention, a s ;i 1lustrated in Figs. 1 to 6; indts r .;the.:i am Z -mad 9 eeel s 3 shaped to conform substantially to the interior of the duct l0. Thus, it is of rectangular outline and of a size slightly smaller than that of the interior of the duct.

So that the frame 22 will be maintained in a vertical position perpendicular to the side walls of the duct l under conditions of angular duct mounting or plant movement, it is pivoted at its top edge for free swinging movement within the duct. Thus, it is supported on a transversely extending rod or shaft 30, the ends of which are journalled in anti-friction bearings 32 which are preferably of the ball bearing type. The bearings 32 are, in turn, supported in brackets 34 which are secured to the side walls of the duct Ill, intermediate mounting plates 35 which are rigid with the duct walls being utilized in the present embodiment to provide increased strength. To insure exact transverse mounting of the shaft whereby free swinging of the frame within the duct obtains, each bracket 34 preferably is pivotally secured to its respective mounting plate as by a bolt 36, and is provided with an adjusting screw 38, operating through a tapped hole in a lug 39 rigid with the plate, whereby to permit individual adjustment of the respective brackets, and hence the positions of the shaft supporting bearings 32.

If desired, further to insure free swinging of the frame 22 under conditions of horizontal tilting, the frame may be equipped with side thrust bearings 40 which, as shown in Figs. 5 and 6, are mounted at each of the lower corners of the frame in engagement with the side walls of the duct l0 and disposed for rotation about a vertical axis.

Should the weight of the frame itself be insufficient to insure its maintenance in vertical position, the frame may be equipped with a weight 42 (Figs. 3 and 5), which, as shown, is attached centrally of the lower transverse member thereof.

To minimize air leakage into the duct ill beneath the frame '22, especially as the frame swings from its position illustrated in Fig. 3 in either direction within the duct l0, there is provided in cooperative association with the free swinging edge of the frame an apron 4|, the upper surface of which is curved about the axis of the shaft 30. The apron 4| is attached to the bottom of the duct l0 and extends from the outer end thereof,overlapping the flange l6, inwardly into the duct to a point slightly beyond the normally expected range of swing of the frame 22. The inner end of the apron 4| is bent downwardly, and is flanged where it is welded or otherwise rigidly secured to the bottom wall of the duct it.

In the present embodiment of the invention, the damper plate 24 is pivotally supported adjacent its lower edge and, when in closed position, bears against the inside marginal edge of the swinging frame 22, a strip 43 of cushioning material, such as felt, being disposed between the engageable portions of the plate and frame for shock-deadening purposes. Preferably, the strip 43 is cemented to the inner face of the transversely extending portions of the frame 22.

To provide a pivotal mounting for the damper plate 24, it is secured to a transverse rod or shaft 44 in any suitable manner, the opposite ends of which are journaled inanti-friction bearings 46. These bearings are also preferably of the ball bearing type, and have their outer races received in brackets 48 welded or otherwise rigidly secured in the lower corners-of the frame .22.

The counterbalancing means 25 which is DlO- vided to oppose the action of the draft on the damper plate 24, includes counterweights 58 which are adjustable in position both horizontally and vertically to permit change of location of the center of gravity of the damper plate and counterbalancing system with respect to the pivotal axis, so that the definite force acting in opposition to the suction on the plate due to the stack draft is maintained for a particular counterweight arrangement. Accordingly, a predetermined draft intensity is maintained through the furnace or boiler. The damper plate, moving in response to the difference between the draft force and the counterbalancing force, is thus effective to compensate for draft fluctuations by varying the effective inlet area of the frame opening 22a.

In the present instance, the counterweights 50 are supported at the ends of a horizontal crossbar 52, the latter being fastened intermediate its ends to a depending supporting arm 54 which is preferably channel-shaped. The upper end of the arm 54 is pivotally connected to the damper plate 24, which as illustrated is accomplished through the use of a pair of brackets 55 and 55 and a pivot pin 51. The bracket 55 is of elongated U-shape and is attached in vertical position centrally of the plate 24. The bracket 55 is also of U-shape, and has its bight portion fixed adjacent the upper end of the bracket 55 so that its arms extend outwardly. These arms and the upper end of the counterweight supporting arm 54 are appropriately apertured to receive the pivot pin 51 which is retained in position in any suitable manner, as by cotter pins 58. This mounting permits free forward and backward swinging of the arm about a transverse horizontal axis and effectively prevents any tendency thereof to rotate or twist about vertical or longitudinal axes.

To permit free fore and aft movement of the depending arm 54 and the frame weight 42, both of which are adapted to extend below the duct I9, the bottom wall of the duct and the apron 4| are provided with registering longitudinally extending slots Ilia and 41a, respectively (Fig. 5).

Each of the counterweights 50 comprises a closed upwardly curved tube of substantially quadrantal form having a heavy metal ball 52 disposed therein which is adapted to move along the tube under the influence of gravity upon movement of the damper plate and counterbalancing system. To enhance the sensitivity of the counterbalancing means, the balls 62 may be floated on a small quantity of mercury as indicated at 64. Bridging the end of the tubes 60 is a bar 66 which is slidably received in a guide 68 rigid with the ends of the crossbar 52. Thus the 'counterweights 50 may be shifted forwardly or rearwardly with respect to the depending arm 54 to produce a corresponding shifting of the center of gravity of the damper plate and counterbalancing system. Each guide 68 is equipped with a set screw 68a by means of which the bar 66 may be clamped within the guide so as to maintain the desired position of the counterweight.

Provision is made for raising and lowering the counterweights 50 so as to vertically adjust the center of gravity of the system with respect to the pivotal axis. To this end, the arm 54 is provided with a series of spaced apertures 69 for the reception of a bolt 10 carried intermediate the ends of the crossbar 52.

As an additional means of adjustment there is provided a thumb screw 12 supported on the deaces-gets p'en'ding arm 54 and 'engageable with the bracket 55; which" is rigid with the damper plate 24. The thumb screw 12 is operable to vary the angular relationship between the depending arm 54 and the plane of the damper plate. When such angular relationship is determined, maintenance thereof is assured by means of lock nuts H disposed on opposite sides of the depending arm and engageable therewith to lock" the screw in the desired position.

It will be evident that the damper plate 24 and the c'ounterbalancing' means are constrained to move in synchronism. As the damper plate 24 swings inwardly in response to an increase in the draft above a certain predetermined value, thus efiectively increasing the air inlet area, the counterweights 50 are swung in a clockwise direc-- tion as viewed in Fig. 3, upwardly and outwardly. Conversely, as the draft decreases, the damper plate and the counterweights swing in the reverse direction. Hence, the control tends to seek a position of balance and thus serves to compensate fluctuations in the draft by controlling the inflow of air into the stack from outside the furnace or boiler.

Initial opening movement of the damper plate 24 takes place immediately upon the draft in tensity exceeding the predetermined desired value, i. e. the counterforce exerted by the counterbalancing means as selected and adjusted, and air enters the duct l at a considerable velocity; hence, the plate is sensitive to even small pres sure fluctuations. However, as the plate is caused to" swing progressively toward its maximum open position, it tends to become less sensitive to changes in the draft, that is to say, its operation becomes lazy. While the closing force exerted by the counterbalancing means increases as the plate 24 moves toward fully open position, the balls 62 and the mercury 64' move along the tubes 6'0 to reduce the rate of increase, thus rendering the plate more sensitively and accurately responsive when open a substantial distance, thereby overcoming any lazy tendencies.

The curvature of the weight-supporting tubes 6*!) controls the action of the balls 62 and the mercury pool 64. The greater the radius of such tubes, the more rapid will be the action of the balls and the mercury, and the more apt will be the noisy banging" of the balls against the tube ends. Decreasing this radius tends to slow the action of the balls and decrease the sensitivity of their response. It has been found that a radius of curvature of approximately 12 inches is the most practical for general application.

With the adjustments hereinbefore described for the counterbalancing means, the control is adaptable for an almost infinite number of different installations and for different operating conditions. It will be apparent that each of the counterweights' 50 may be adjusted on the arm 54 transversely of the shaft 30. If the two counter"- weights are both adjusted to their outermost positions, a heavy closing action will be obtained. If the counterweights are both adji-ls-ted' to their innermost positions, a light closing forceis exertedwhich is sufii-cient barely tohold the plate- 2'4 against the swinging frame 22. Any desired intermediate adjustment within the wide range defined by these limits may be attained.

Turning now to Figs. 7" to 9, inclusive, of the drawings, the modifiedfform of the inventionthere shown may be termed an inverted control, as compared to thefor'm just described. For the sake of brevity, similar elements are denoted by the-primes of like reference numerals. This draft control as before includes a duct Ill rigidly secured over an opening lid in the vertical wall of a stack or flue l-Z', and having an angularly disposedforward end [6" just like that in the first embodiment described. In this embodiment, however, the damper plate 2-4 of the device is pivoted at its upper edge and on the same axis as is the swinging frame 22' and-the counter balancing means for the damper plate extends oppositely from that in the embodiment here-- inbeforedescribed. This form or the invention, then, may be termed an: inverted control, as com-- pared to thefirst form described. r v

To pivotally support both the swinging-frame 2'2 and the dam er plate 24-" on a common axis, a single transverselydisposed rod or shaft 30' is utilized. To support the damper plate 24" for pivotal movement with respect to the swinging frame 2-2 the latter is provided with apertured supporting members or brackets rigid therewith for the reception of additional anti-friction bearing elements 82. The damper plate 24" is rigidly secured to the shaft 30' and the latter, while extending through openings in the sides of the swingingv frame, is free to rotate therein.-

The counterbalanci-n means 26" in this embodiment includes the saineelements as previously set forth for the first embodiment described; however, their action, due to the inverted relationshipof the damper plate and swinging frame, is the reverse of that previously set" forth. This necessitates only a simple rearrangement of elements; and a singlestructural modification. It will be noted that most of the weight of. the counterbalancing means is disposed above the plane of thepivotal axis of the systemincluding the damper plate and counterbalancing' means. Thus the adjusting" screw 12'' is rotatably an:- chored adjacent the upper end of the damper plate bracket 55- to prevent the counterweight supporting arm 54" from swinging in a counterclockwise direction, as shown, about the pivotalaxis and out of operative relation with respect to the damper plate.

In the other modified form of the invention as illustrated in Figs. 10 and 1-1 wherein similar ele-'- ments are denoted by the double primes of like reference numerals, the duct l0 and the elements of the control rigid therewith, including the rear marginal supporting flange l4", the flange l6 defining the air inlet opening 18-", and the apron 41-", are mounted in a position inverted with respect to those shown in the preceding embodiments. The damper plate 24 and the counterbalanci-ng means 2-6 therefor are disposed and operate in the same manner as described for the first form of the invention, namel'y, that illustrated in Figs. 1 to 6, inclusive. In this form, however; the swinging frame 22" is adapted for movement about atransverse axis 30" which is disposed adjacent the bottom edge instead of the top edge of the frame.- The pivotal mountings of both the swinging frame and the damper plate are the same as described for the second form of the invention, namely, that illustrated in Figs; 7 to 9, inclusive.

Since the frame 22" extends upwardly from its pivotal axis, additional. counterbalanc'ing meansfor it is provided. Thus,- adjacent each of itsside; edges, the' frame 22" has attached thereto apair or depending arms =86 on which. are supported relatively heavy. counterweights- 88. If desired, these weights may be adjustably supported on the arms 86 by means oi slides 89 7. through which the arms are passed. To permit clearance of the bottom wall of the duct l", each of the arms 85 has an intermediate U- shaped portion 860, formed therein near its upper end. As shown, however, the upper and lower extremities of the arms are disposed parallel to the plane of the side members-of the swinging frame 22". The counterbalancing weights 88, of which there may be any suitable number, may be alternately arranged to front and back thereof for proper adjustment of the center of gravity of this counterbalancing means, to assure maintenance of the frame 22" in a vertical position.

From the foregoing it can be seen that only minor changes of structure and simple rearrangement of elements are necessary to permit installation of draft control devices constructed in accordance with the present invention in almost any furnace or boiler system that might be encountered. The illustrative embodiments demonstrate that rotation of the damper plate and the swinging frame may be attained about the same or about separate axes and disposed at the top or at the bottom of the duct. As between the second and third exemplary forms of the invention illustrated, the change necessary is the addition of the counterweights 88 for the swinging frame so that the same is maintained in vertical position. The counterbalancing means for the damper plates renders them self-closing. The suction of the draft tends to move the plate into open position against the action of the counterbalancing means and the latter is accurately adjustable over a wide and finely graduated range, fineness of adjustment being attained by the use of the thumb screws 12, 12' or 12 which alter the angular relation between the counterweight supporting arms and the damper plate. In the inverted control, when the arm 54' is adjusted rearwardly of the plane of the plate, it operates to move the damper plate toward closed position. In the normally operating controls, theforms illustrated in Figs. 1 to 6 and in Figs. 10 and 11, this action is reversed so that if the arm 54 or 54" and the counterweights or 50" attached thereto are angularly adjusted outwardly from the plane of the plate, the action of the counterbalancing means will be to resist a substantial draft before permitting opening of the damper plate in response to draft suction.

The farther away from the pivotal axis of the damper plate the counterweights are moved along the arm 54, the greater will be the leverage and consequently the effect on the action of the damper plate.

By adjusting the counterweights, jointly or individually backward or forward in relation to the crossbar, a fairly critical counterbalancing adjustment can be made. Positioning of the weights at opposite ends of their supporting bars and relative to the crossbar effects great sensitivity of the damper plate at or near its closed position, making it responsive to very slight barometric changes and very gentle in its action. With the counter-weights side by side and at their rearmost positions in relation to the crossbar, the damper plate will just barely close against the swinging frame. Conversely, with the weights side by side and at their foremost positions in relation to the crossbar, the closing action on the damper plate 24 is increased to maximum and the plate is held against the swinging frame until a considerable suctional force of draft obtains. In the inverted control, these adjustments will have the reverse effect' a The wide range of adjustment of the counterbalancing means, together with the available fineness thereof, is of great importance due tothe many prevailing sizes and heights of chimneys,

the widely varying characteristics of fuels and heat generating plants together with the differing requirements of specific installations as to space limitations and as to special purposes.

W e claim as our invention:

1. An automatic draft control comprising, in combination, a duct of rectangular cross section adapted to be secured over an opening in a stack and open at its free end, a rectangular frame fitting closely within the duct adjacent the open end thereof and having an inner marginal flange defining a rectangular air inlet opening, means for pivotally supporting said frame for free swinging movement so that the frame will maintain a vertical position regardless of angular disposition of the duct, a damper plate pivotally supported at one edge thereof on said frame and normally engaging the inside of said flange to clos said opening, said plate being swingable about a horizontal axis inwardly from said opening in response to a draft increase in said stack, and counterbalancing means operatively connected with said plate and tending to urge the same into closed position.

2. An automatic draft control comprising, in combination, a duct adapted to b secured over an opening in a stack and havin an air inlet opening in its outer end, a frame pivotally supported adjacent its top edge and adjacent the top wall of the duct so as to maintain a vertical position transversely of the duct regardless of angular disposition of the latter. and a damper plate pivoted on said frame and counterbalanced to normally bear thereagainst so that said frame and plate are normally effective to close off said air inlet opening, said counterbalanced damper plate being movable into an open position in response to a draft increase within the stack to admit air directly into the stack whereby to maintain a substantially constant draft.

3. An automatic draft control, comprising, in combination, a duct adapted to be secured over an opening in a stack, a frame having an air inlet opening therein pivotally supported adjacent its lower edge and adjacent the bottom wall of the duct, counterbalancing means for said frame effective to maintain the frame in a vertical position transversely of the duct regardless of angular disposition of the latter, and a damper plate pivoted on said frame and counterbalanced to normally bear thereagainst to normally close said air inlet opening, said damper plate being movable into an open position in response to a draft increase within the stack to admit air directly into the same.

4. An automatic draft control comprising, in combination, a duct having an open outer end, a frame having an air inlet opening pivotally supported at its lower edge within the duct and adjacent the open end thereof, counterbalancing means operative to maintain said frame in a vertical position transversely of the duct, and a damper plate pivoted on said frame and counterbalanced to normally bear thereagainst to close off said air inlet opening, said damper plate being movable into an open position in response to a draft increase within the stack to admit air directly into the same, the counterbalancing means for said frame including an arm fixed at one end to said frame and formed to extend through the open end of the duct and clear the 9 bottom wall thereof and to extend substantially below the pivotal axis of said frame, and a weight secured adjacent the free end of said arm.

5. An automatic draft control comprising, in combination, a duct, a frame mounted in said duct and supported for free swingin movement about a horizontal axis so as to maintain a vertical position and having an air inlet opening therein, a damper plate pivotally mounted on said frame on a horizontal axis disposed adjacent the 10 bottom of said frame for inward movement with respect to both theframe .and duct to control the effective area of said opening, and counterbalancing means tending to maintain said plate in closed position.

6. An automatic draft control comprising, .in combination, a duct, aframe mounted in said duct andxsupported for fre swinging movement about a horizontal axis so as to maintain a vertical position and having an air inlet opening therein, a damper plate pivotally mounmd in said" frame on a horizontal axis disposed adjacent the top of said frame for inward movement to control the effective area of said opening, and counterbalancing means tending to maintain said plate in closed .25 position.

7. An automatic draft'control comprising, in combination, a duct, a frame mounted in said duct and supported for free swinging movement about a horizontal axis adjacent one edge there of so as to maintain a vertical position transversely of the duct and having an inlet opening therein, a damper plate pivotally mounted in said frame on a horizontal axis adjacent the edge of the frame opposite its pivotal axis to control=i the effective area of said opening, and counterbalancing means tending to maintain said plate in closed position.

8. An automatic draft control comprising, in combination, a duct, a frame mounted in saidlltO duct and supported for free swinging movement about a horizontal axis disposed adjacent one edge thereof so as to maintain a vertical position transversely of the duct and having an air inlet opening therein, a damper plate pivotally 4 mounted in said frame on the same horizontal axis as said frame but being swingable thereon independently of the frame to control the effectiv area of said opening, and counterbalancing means tending to maintain said plate in closed position.

9. An automatic draft control comprising, in combination, a duct adapted to be secured over an opening in a stack, a frame transversely disposed in said duct and pivotally mounted at one end thereof for free swinging movement to maintain a vertical position and having an air inlet opening, and means interposed between the free end of the frame and th wall of th duct adiacent thereto effective to minimize leakage of air 0 therebetween, a damper plate pivotally mounted on said frame and responsive to draft fluctuations to control the effective area of said air inlet opening, and counterbalancing means for said damper plate tending to maintain the same in closed position.

10. An automatic draft control comprising, in combination, a duct, a frame transversely disposed in said duct and pivotally mounted at one end thereof for free swinging movement to maintain a vertical position and having an air inlet opening, an apron rigid with the wall of the duct adjacent the free end of the frame and having the surface thereof adjacent said free frame end formed to the arc traversed by the free frame plate tendinggto maintain the same in end whereby leakageof air into the duct is minimized, a damper plate pivotally mounted on said frame and. responsive to draft fluctuations to control the effective area of said air inlet opening.

11. An automatic draft control comprising-,-=in combination, an open-ended duct adapted to be secured over an opening in a stack, a frame transversely jdisposedin said duct and pivotally mounted for free swinging movement so as to maintain a vertical position, said frame having an inner marginal flange defining an air inlet opening, a, damper platepivotally mounted on said frame and responsive to draft fluctuationscontrol the effective area'of said air inlet opening, and counterbalancing means for said damper closed position. 1

12. An automatic draft control comprising, in combination, a duct, ragframe fitting withirrsaid duct and :having an air.,inl'et-opening, means for pivotally supporting-said frame for free swinging movementv about a generally horizontal axis extending transversely thereof, a damper plate mounted in said frame for swinging adjustment about a generally horizontal axis for controlling the effective area ofsaid opening, andcounterweight means operatively connected to said, plate, said counterweight means being adjustable to alter the center of gravity of the system including said damper plate andcounterweight means with respect to the-pivotal axisof said damper plate whereby to adjusttheldegree of draftintensity necessary to effect movement of said damper plate into' an :open position.

13.. An automatic draft control comprising-tin combination, "a duct, a frame defining an 'air inlet opening and mounted for freeswinging movement to maintain a vertical position, -a damper plate disposed in operative relation tosaid opening, means on said frame supporting said plate for swinging movement; about a horizontal axis extending transversely of said frame, and counterbalancing means operatively connected with said plate and adapted. to move the "same into closed position with respect to: said opening, said 5 counterbalancing means including an arm pivotally secured to said plate, a generally horizontal crossbar adjustablyasecured 'to said arm and having a guide member thereon, angupwardly curved tube, a guide bar rigid with said tube and slidably received in said guide member for adjustment transversely of said plate axis, and a weight freely movable in said tube in response to gravity.

14. An automatic draft control comprising, in combination, a frame pivotally supported for free swinging movement so as to maintain a vertical position and having an air inlet opening, a damper plate pivotally supported on said frame for rotation about a horizontal axis in operative relation to said opening, an arm pivotally secured at one end to said plate, a crossbar adjustably secured adjacent the free end of said arm for movement therealong and having a generally horizontal guide member adjacent'each of its ends, and a pair of counterweights each including a guide bar slidably received in said guide members and adjustable therein transversely of said plate axis, an upwardly curved tube rigid with said guide bar and a weight freely movable in said tube in response to gravity.

15. An automatic draft control comprising, in combination, a frame pivotally supported for free swinging movement so as 'to maintain a vertical position and having an air inlet opening therein,

a damper plate pivotally supported on said frame Y for rotation about a horizontal axis in operative relation to said opening, an arm pivotally secured at one end to said plate, a crossbar adjustably secured adjacent the free end of said arm for vertical adjustment therealong and having a generally horizontal guide member adjacent each 'of its ends, a pair of counterweights each including a guide bar slidably received in one of said guide members topermit adjustment of its 1 position transversely of said plate axis, an upwardly curved tube rigid with said guide bar and a weight freely movable in said tube in response to gravity, and means operatively associated with said armand said plate effective to vary the angular relationship between the two.

16. An automatic draft control comprising, in combination, a duct, a frame disposed within said duct and defining an air inlet opening, means suppcrting'said frame adjacent one side thereof for free swinging movement about an a frame supported adjacent one end thereof on said shaft and having an air inlet opening, antifriction bearings journaled in said shaft to permit free swinging movement of it and said frame so that the latter maintains a vertical position, supporting brackets for said bearings adjustable in position to insure transverse disposition of'the shaft and frame within said duct, side thrust bearings supported on said frame adjacent the free end thereof and engageable with the side walls of the duct to prevent dragging of the frame thereon, and a counterbalanced damper plate pivotally supported on said frame and engageable therewith to close said opening.

T 18. An automatic draft control comprising, in combination, a duct, a frame mounted in said duct and supported for frees'winging movement about a horizontal axis adjacent one edge thereof soas to maintain a vertical position transversely of the duct and having an air inlet opening therein, a shaft extending transversely of said frame, anti-friction bearings supported on said frame and journaling said shaft, a damper plate rigid with said shaft and operative to control the effective area of said frame opening, and counterbalancing means operatively connected with said plate tending to maintain the same in closed position.

19. An automatic draft control comprising, in combination, a duct, a shaft extending transversely of the duct, a frame supported on said shaft and having an air inlet opening therein, anti-friction bearings supported on said duct and on said frame and journaled in said shaft, 2. counterbalanced damper plate rigid with said shaft and disposed within said frame and operative to control the effective area of said opening, said bearings permitting free swinging movement of said frame so as to maintain a vertical position and movement of said damper plate independently of said frame.

20. An automatic draft control comprising, in combination, a frame pivotally supported for free swinging movement to maintain a vertical position and having an air inlet opening, a damper plate pivotally supported on said frame for movement about a horizontal axis and operative to control the effective area of said opening, and counterbalancing means operatively connected to said plate tending to maintain the same in closed position with respect to said opening, said counterbalancing means including a counterweight disposed on the opposite side of said axis from said plate, said counterweight including a quadrantal tube, a weight and a quantity of mercury movable in said tube in response to gravity.

WILLIAM B. STEPHENSDN. JAMES S. LEE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,276,728 Johnson et al Mar. 17, 1942 2,319,652 Young May 18, 1943 

